1. Field of the Invention
This invention relates to a toner for developing electrostatic charge latent images in the electrophotographic method or the electrostatic recording method.
2. Related Background Art
In toners for developing electrostatic charge images, since it is difficult to obtain stable chargeability with the binder resin alone used therefor, it has been practiced to add a charge controllable substance such as a dye or a pigment for controlling the toner to desired triboelectric chargeability.
As the compound for controlling the positive charging of the toner practically applied to this field of art, there is a nigrosine type dye. On the other hand as the compound for controlling negative chargeability of the toner, there may be included metal containing compounds as disclosed in Japanese Patent Publication Nos. 45-26478 and 55-42752. These compounds have excellent characteristics among the charge controllable substances proposed in the prior art with respect to the performance of imparting charges to toner particles, and could provide a toner capable of giving practically satisfactory images in as copying machine or a page printer under ordinary environmental conditions.
However, under the progress of personalization, speed acceleration, multifunctionalization in image forming devices according to the electrophotographic method or the electrostatic recording method, it has been demanded to have a toner which has more excellent environmental stability, good durability stability and can give an image having high image density without fog, enriched in resolving power with sharp contrast and also excellent in gradation reproducibility. Various developing method, including not only the positive developing method, the analog developing method, but also the reversal developing, the digital developing, the low potential developing have been used.
With miniturization and personalization, toners are used increasingly in places where there is no air conditioning under high temperature and high humidity in tropical districts or under low temperature and low humidity in inland districts, and must give stably images of high quality even under severe environment. Further, with acceleration of speed, images of high quality must be provided stably, while standing use of a large amount of the toner at one time and continuous use over a long term.
The performance demanded for the toner is not only developability, but various starting materials have been employed for improving fixing characteristics, off-set resistance, cleaning characteristics, antiblocking characteristics. With such improvements, the trielectric charges on the material are greatly changed and the function of the charge controlling agent is not satisfactory only with the function of enhancing the charges of the toner, but it has been demanded to "control" constantly the charged amount of the toner.
Under such situation, the image forming method employing a magnetic toner containing magnetic powder in the toner has been frequently used. With the progress of such technique, it has been desired to have a magnetic toner having well controlled chargeability.